Have you ever been captivated by those naked-eye 3D large screens on bustling commercial streets?
A spaceship slowly sails out of the screen, a panda leans out—these images seem to emerge beyond the screen, three-dimensional and stunning.
In daily life, what we see on screens is all two-dimensional. So how do naked-eye 3D large screens make images "break out" of the screen? This counterintuitive visual experience is actually a visual deception.
Naked-eye 3D refers to the ability to directly perceive three-dimensional visual effects with the naked eye without relying on external devices such as glasses or helmets. The core principle of this technology leverages our inherent parallax characteristic.
The human visual system has a distance of approximately 60mm between the two eyes. When viewing an object, the images formed on the retinas of the left and right eyes have a certain degree of horizontal difference.
If you hold your index finger in front of your eyes, close your right eye and look with your left, then close your left eye and look with your right, you'll notice that the position of your index finger relative to the distant background changes. This phenomenon is parallax.
Since there is parallax between the two eyes, why don't we see double images but instead perceive three-dimensional objects?
It's because after the eyes receive information from two different images, the brain automatically processes this information, allowing us to ultimately perceive a three-dimensional picture.
Naked-eye 3D technology simulates this natural process: through special display technology and image processing methods, it projects images from different viewing angles on the screen simultaneously, enabling our left and right eyes to each receive distinct images.
In this way, when the brain processes these images, it is deceived into synthesizing them into a three-dimensional image, as if the real world is unfolding right before our eyes.
For the screen, the key challenge of naked-eye 3D technology is to ensure that the left and right eyes see different images. Currently, there are three mainstream technical approaches:
The principle of this technology can be understood as installing a layer of venetian blinds (i.e., slit gratings) in front of the screen, dividing the displayed image into extremely fine vertical stripes. The presence of this grating blocks part of the light.
When the image intended for the left eye is displayed on the screen, the stripes block the right eye; conversely, for the right eye, the grating stripes block the image meant for the left eye. By separating the visible images for the two eyes, the viewer perceives a 3D effect.
(Note: 3D glasses also use the principle of light barriers.)
The technical principle of lenticular lenses involves adding a layer of lenticular lenses in front of the screen. By altering the light path, the lenses can refract each pixel in different directions.
Through algorithms, the images for the left and right eyes are precisely interleaved on the screen. The lens layer then guides these two sets of images to the viewer's left and right eyes respectively. After the brain receives these two parallax images, it fuses them into a three-dimensional vision.
Unlike the passive light refraction through lenses, this technology actively controls the emission direction of light from each pixel, projecting images for the left and right eyes directly into the corresponding eyes, allowing the human eye to perceive a 3D effect.
Ordinary screens emit light in all directions—no matter where you stand in front of the screen, you see the exact same two-dimensional image.
The core of naked-eye 3D technology lies in "separating viewing angles" and providing two parallax images for the left and right eyes to induce the brain to perform three-dimensional synthesis, which is the key to achieving the three-dimensional effect.
Technologies such as parallax barriers and lenticular lenses lay the hardware foundation for naked-eye 3D screens, but content is also crucial to presenting a three-dimensional visual experience.
When rendering screen content, an optimal viewing angle is preset, and three-dimensional images are constructed using perspective principles.
In offline scenarios, you'll find that almost all naked-eye 3D large screens are installed at 90° corners of buildings—and this is no coincidence.
Our eyes and brain judge the distance and shape of objects through perspective and shadows, and a flat screen can hardly provide strong depth cues.
Presenting two adjacent sides of an object on two vertical planes fully conforms to the perspective law of observing a real cube placed in a corner in reality. The brain will automatically "stitch" the images on these two surfaces and mentally construct a complete three-dimensional object.
When a virtual cube is supposed to break out of the screen, the rendered image strictly follows the perspective law of "near-large and far-small": the part closer to you is drawn very large, while the part farther away is drawn small.
This perspective principle realizes the sense of distance between the virtual object and the screen through visual scaling, making the object appear as if it is protruding from the screen.
In the design of screen content, a fictional black screen frame is usually created, or the edge of the building's corner is directly used as an occluder, allowing the object that intends to break out of the frame to cross this boundary.
Take the naked-eye 3D display screen at Chengdu Taikoo Li as an example. When displaying a spaceship image, although the actual boundary of the screen is far beyond the visible frame, the illusion of breaking out of the screen is created by precisely controlling the brightness and boundary of the image.
(Note: The windows of the adjacent building are replicated in the image to further enhance the realism of the frame.)
The display of naked-eye 3D screens breaks the limitations of traditional two-dimensional planes by simulating the perspective relationship of real objects and combining it with the parallax of the left and right eyes, thus simulating the three-dimensional perception of the real world.
It's like a sensory trick—not creating true three-dimensionality, but stimulating the sensory cues needed for the brain to "perceive" three-dimensionality.
In an era of scarce attention, this technology provides an unprecedented visual experience and brings new opportunities for commercial applications. Whether it's brand communication, urban landscapes, or interactive marketing, it has opened up a whole new realm of imagination.
